Final answer:
Josef Stalin was the key figure who led the Soviet Union in spreading communism during the Cold War.
Step-by-step explanation:
The key figure during the start of the Cold War who led the Soviet Union as it spread communism to the post-WWII world was Josef Stalin. Stalin served as the General Secretary of the Communist Party of the Soviet Union from 1922 until his death in 1953. He implemented policies that aimed to expand Soviet influence and establish communist governments in Eastern Europe, leading to the division between the Eastern Bloc and Western powers during the Cold War.
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